add quickstart for Debian in readme

Should address #14 even though it's not "quite" a one-liner, since it also covers installing the dependencies.

README.md

@@ -4,6 +4,19 @@ This is a version manager for [RGBDS](https://github.com/gbdev/rgbds). It is a p
 
 \* Bash script, at the moment. Compatibility with other shells is not guaranteed.
 
+## Quickstart (Debian)
+```sh
+sudo apt install -y libpng-dev pkg-config build-essential bison git curl
+sudo sh -c 'curl https://raw.githubusercontent.com/gbdev/rgbenv/master/rgbenv > /usr/local/bin/rgbenv'
+sudo chmod +x /usr/local/bin/rgbenv
+yes | rgbenv install 0.7.0
+rgbenv use 0.7.0
+echo 'export PATH=$HOME/.local/share/rgbenv/default/bin:$PATH' >> .bashrc
+source .bashrc
+
+rgbasm -V
+```
+
 ## What does it do?
 
 * Installs or uninstalls a specific version of the RGBDS suite.